Pedicellariae are small pincer-like organs found across echinoderms, normally used to keep the body surface clear of settling larvae and debris. In Toxopneustes they are enlarged, numerous and venomous, each consisting of three hinged valves on a stalk with a venom gland at the base.
On contact the valves close and grip. The head can then detach from its stalk while still attached to the victim, and the jaws continue to work and release venom independently of the animal. Human envenomation reports describe severe pain, and there are historical accounts of respiratory difficulty and paralysis in serious cases, though well-documented fatalities are very few.
Divers are often warned about long-spined urchins such as Diadema, whose danger is mechanical puncture and mild irritation. The flower urchin is the reverse case: harmless-looking, soft to the eye, and genuinely venomous. The composition and mode of action of its venom are only partly characterised, and the toxins responsible for the systemic effects are not fully identified.